Cyclodextrin is capable of including various compounds within its tubular cavity and such inclusion compounds can be used as adsorption/separating agents. However, cyclodextrin is soluble not only in water but also in certain organic solvents. It has therefore been difficult for cyclodextrin to include a compound from various types of systems for isolation. Under such circumstances, it has been proposed to use cyclodextrin as an insoluble high-molecular weight compound.
Such approach for using cyclodextrin as a high-molecular weight compound includes: use of a reaction product of chloromethylated polystyrene with a cyclodextrin derivative as described in Japanese Unexamined Published Patent Application Nos. 61290/1979 and 61291/1979; use of an immobilized cyclodextrin amino derivative prepared by reacting an insoluble high-molecular weight substance with a cyclodextrin derivative as described in Japanese Unexamined Published Patent Application No. 227906/1984; and use of cyclodextrin crosslinked with epichlorohydrin to form a high-molecular weight compound wherein the residual hydroxyl groups in cyclodextrin being converted to other functional groups, or cyclodextrin immobilized to the terminal functional groups of a copolymer by polymer reaction, as described in Japanese Unexamined Published Patent Application No. 275102/1987.
However, in the case of immobilizing cyclodextrin on polymers by the polymer reaction, the extent of immobilization is so small that the aforementioned function of cyclodextrin can hardly be expected. The crosslinked product has a three-dimensional network structure, so it is difficult to expect cyclodextrin to retain the ability to make a tubular structure. Further, the conversion of cyclodextrin into an insoluble polymer has been causeing problems such as the waste.
Based on the above-described characteristics of cyclodextrin, an immobilized membrane containing cyclodextrin is expected to have unique separating, permeating and other abilities. Further, the cycodextrin supported on a polymer is expected to have various physical properties that could not been attained by cyclodextrin alone, thereby extending the applicability of cyclodextrin. Hence, there has been a need for a method of easily preparing a membrane containing cyclodextrin.
For the preparation of such cyclodextrin membranes, Japanese Unexamined Published Patent Application No. 232210/1985, discloses a method in which a polymer comprising the crystal of a cycloextrin inclusion compound and a compound containing isocyanate groups is cast onto a commercial ultrafiltration membrane; Japanese Unexamined Published Patent Application No. 258702/1987 discloses a method in which cyclodextrin is reacted with various monomers and thereafter copolymerized with an acrylonitrile derivative to produce a polymer which is then processed into a membrane by known techniques.
However, the method disclosed in Japanese Unexamined Published Patent Application No. 232210/1985 has the disadvantage that the cyclodextrin membrane produced can not be employed as a membrane of the polymer per se, and the method disclosed in Japanese Unexamined Published Patent Application No. 258702/1987 has the disadvantage that the degree of incorporation of cyclodextrin into the polymer membrane is not sufficiently high.
An object, therefore, of the present invention is to provide a cyclodextrin polymer having an increased amount of cyclodextrin unit immobilized to achieve marked improvement in their function.
Another object of the present invention is to provide a cyclodextrin polymer which is insoluble in water, etc. but capable of being decomposed by an enzyme, by using a specific high-molecular weight compound, thereby said cyclodextrin polymer can be used as a degradable polymer.
Still another object of the present invention is to provide a cyclodextrin membrane which contains cyclodextrin in a high proportion and yet can be used alone as a membrane.